Estimation of multiple flexibilities of an articulated system using inertial measurements
Résumé
For many articulated systems (i.e. systems com- posed of several mechanically connected objects), the assumption of full rigidity is only a mere approximation. The various flexibilities of the structure, if not accounted for, all hinder the positioning ability of the device, by generating biases in the estimations determined from rigid models. In this paper, we propose a sensor-based methodology for estimating the flexibilities of an open kinematic chain. To estimate the real position and orientation of the elements of the system, we reconcile data from Inertial Measurement Units (IMU) with the kinematics of the rigid system. We show that, under a model of punctual, spring-like deformations, this methodology allows one to observe all the deformations, if one IMU is installed downstream of each deformation in the chain. We design and test such an observer in simulation and on an exoskeleton, where it proved a suitable way of estimating the position of the flying foot. Experimental results, validated against a motion capture device, demonstrate the ability of this observer to fully capture the dynamics induced by these flexibilities.